<template>
  <ul class="alphabet">
    <li class="alphabet-items" 
    v-for="(value,key) in cities" :key="key"
    :ref="key"
    @click="scrollTarget"
    @touchstart="handleTouchStart" 
    @touchmove="handleTouchMove" 
    @touchend="handleTouchEnd" 
    >{{key}}</li>
  </ul>
</template>

<script>
export default {
  name: 'CityAlphabet',
  props:{
    cities: Object
  },
  data () {
    return {
      scrollStatus:false,
      startY:0,
      timer:null
    }
  },
  computed:{
    letters () {
      const arr = []
      for(let key in this.cities){
        arr.push(key)
      }
      return arr
    }
  },
  updated () {
    this.startY = this.$refs['A'][0].offsetTop
  },
  methods:{
    scrollTarget (e) {
      const value = e.target.innerText
      this.$emit('scrollTarget',value)
    },
    handleTouchStart () {
      this.scrollStatus = true
    },
    handleTouchMove (e) {
      if(this.scrollStatus){
        if(this.timer){
          clearTimeout(this.timer)
        }
        this.timer = setTimeout(()=>{
          const touchY = e.touches[0].clientY - 79
          const index = Math.floor((touchY - this.startY) / 20)
          if(index>=0 && index<this.letters.length){
            this.$emit('scrollTarget',this.letters[index])
          }
        },20)
      }
    },
    handleTouchEnd () {
      this.scrollStatus = false
    }
  }
}
</script>

<style lang="stylus" scoped>
@import '~styles/varibles.styl';
.alphabet{
  display: flex
  flex-direction: column
  justify-content: center
  position: absolute
  top: 1.58rem
  right: 0
  bottom: 0
  width: .4rem
  .alphabet-items{
    line-height: .4rem
    text-align: center
    color: $bgColor
  }
}
</style>
